This invention relates to a slurry hydroprocessing process for upgrading a hydrocarbon feedstock containing nitrogen and sulfur using bulk multimetallic catalyst comprised of at least one Group VIII non-noble metal and at least two Group VIB metals wherein the ratio of Group VIB metal to Group VIII metal is about 10:1 to about 1:10.
Hydroprocessing includes a variety of processes wherein the quality of feedstocks, typically petroleum feedstocks, is improved by treating the same with hydrogen in the presence of a hydrotreating catalyst. Various types of reactions may occur during hydrotreating. In one type of reaction, mercaptans, such as disulfides, thiophenes, benzothiophenes and dibenzothiophenes are desulfurized. The thiophenes, mercaptans and disulfides are representative of a high percentage of the total sulfur in lighter feedstocks. Benzothiophenes and dibenzothiophenes appear as the predominant sulfur forms in heavier feeds such as light catalytic cracker cycle oil (LCCO) and vacuum gas oils (VGO). Hydroprocessing also removes nitrogen from various nitrogen compounds such as carbazoles, pyridines, and acridines. Hydrotreating can also hydrogenate aromatic compounds, existing as condensed aromatic ring structures with 1 to 3 or more aromatic rings such as benzene, alkyl substituted benzene, naphthalene, and phenanthrene.
The most common hydroprocessing process utilizes a fixed bed hydrotreater. A fixed bed system, however, has several disadvantages or inherent limitations. At relatively low temperatures and employing a conventional catalyst, a fixed bed system is characterized by relatively low reaction rates for the hydrogenation of multi-ring aromatics and the removal of nitrogen and sulfur in the material being treated. On the other hand, at relatively higher temperatures, a fixed bed system suffers from equilibrium limits with respect to the degree of aromatics hydrogenation.
Another limitation of a fixed bed system is the difficulty in controlling the temperature profile in the catalyst bed. As a result, exothermic reactions may lead to undesirably higher temperatures in downstream beds and consequently an unfavorable equilibrium. Still a further limitation of a fixed bed system is that a high pressure drop may be encountered, when employing small particle catalysts to reduce diffusion limits. Finally, a fixed bed system suffers from catalyst deactivation, which requires periodic shutdown of the reactor.
Hydroprocessing processes utilizing a slurry of dispersed catalysts in admixture with a hydrocarbon oil are generally known. For example, U.S. Pat. No. 4,952,306 teaches a slurry process for hydrotreating mid-distillates using a catalyst comprising catalyst particles 1 micron to xe2x85x9 inch in average diameter and characterized by a predefined catalyst index as set forth in the claims.
Also, U.S. Pat. No. 4,557,821 to Lopez et al discloses hydrotreating a heavy oil employing a circulating slurry catalyst. Other patents disclosing slurry hydrotreating include U.S. Pat. Nos. 3,297,563; 2,912,375; and 2,700,015, all of which are incorporated herein by reference.
While conventional slurry hydroprocessing has met with varying degrees of commercial success, there still remains a need in the art for processes and slurry catalysts that result in improved yields and selectivity.
As the supply of low sulfur, low nitrogen crudes decrease, refineries are processing crudes with greater sulfur and nitrogen contents at the same time that environmental regulations are mandating lower levels of these heteroatoms in products.
In one approach, a family of compounds, related to hydrotalcites, e.g., ammonium nickel molybdates, has been prepared. Whereas X-ray diffraction analysis has shown that hydrotalcites are composed of layered phases with positively charged sheets and exchangeable anions located in the galleries between the sheets, the related ammonium nickel molybdate phase has molybdate anions in interlayer galleries bonded to nickel oxyhydroxide sheets. See, for example, Levin, D., Soled, S. L., and Ying, J. Y., Crystal Structure of an Ammonium Nickel Molybdate prepared by Chemical Precipitation, Inorganic Chemistry, Vol. 35, No. 14, p. 4191-4197 (1996). The preparation of such materials also has been reported by Teichner and Astier, Appl. Catal. 72, 321-29 (1991); Ann. Chim. Fr. 12, 337-43 (1987), and C. R. Acad. Sci. 304 (II), #11, 563-6 (1987) and Mazzocchia, Solid State Ionics, 63-65 (1993) 731-35.
Consequently, a need exists for increasingly efficient desulfurization and denitrogenation catalysts.
In accordance with the present invention there is provided a slurry hydroprocessing process which comprises hydroprocessing a hydrocarbon feedstock containing nitrogen and sulfur, at slurry hydrotreating conditions, in the presence of a hydrogen containing treat gas and in the presence of a bulk multimetallic catalyst comprised of at least one Group VIII non-noble metal and at least two Group VIB metals and wherein the ratio of Group VIB metal to Group VIII non-noble metal is from about 10:1 to about 1:10.
In a preferred embodiment the bulk multimetallic catalyst is a BMCatalyst bulk catalyst, said catalyst being represented by the formula: (X)b(Mo)c(W)dOz; wherein X is a non-noble Group VIII metal, and the molar ratio of b(c+d) is 0.5/1 to 3/1; the molar ratio of c:d is xe2x89xa70.01/1; and z=[2b+6(c+d)]2, thereby resulting in a feedstock with reduced levels of both nitrogen and sulfur.
In another preferred embodiment of the present invention the Group VIII non-noble metal is selected from Ni and Co.
In still another preferred embodiment of the present invention the Group VIII metal is Ni, and the X-ray diffraction pattern of the catalyst is essentially amorphous with crystalline peaks at d=2.53 Angstroms and d=1.70 Angstroms.
In yet another preferred embodiment of the present invention the molar ratio of b: (c+d) is 0.75/1 to 1.5/1 and the molar ratio of c:d is 1/10 to 10/1.
In still another preferred embodiment of the present invention the distillate feedstock is a product of petroleum, synfuel, coal, shale oil, bitumen, or a tar sand conversion process.
In another preferred embodiment of the present invention the distillate boiling range feedstock boils in the range of about 175xc2x0 to about 400xc2x0 C.
In a preferred embodiment of the present invention the Group VIII non-noble metal is nickel.
In another preferred embodiment of the present invention the feedstock is hydroprocessed in the presence of the bulk multimetallic catalyst prepared by steps that comprise:
(a) adding to a hydrocarbon feedstock having a Conradson carbon content up to about 50 weight percent, one or more thermally decomposable metal compound in an amount sufficient to provide the ratio of atoms of feedstock Conradson carbon, calculated as elemental carbon, to atoms of metal constituents of said one or more thermally decomposable metal compounds of less than about 750 to 1, said metal constituent being at least one Group VIII non-noble metal and at least two Group VIB metals;
(b) heating said thermally decomposable metal compound within said feedstcok at an elevated temperature in the presence of a hydrogen-containing gas to produce a solid high surface area catalyst comprised of at least one Group VIII non-noble metal and at least two Group VIB metals wherein the ratio of Group VIB metal to Group VIII non-noble metal is about 10:1 to about 1:10; and
(c) recovering said high surface area catalyst.